1. Field of the Invention
The present invention relates to a three-dimensional map display system that concurrently uses a plurality of map data to display a three-dimensional map.
2. Description of the Related Art
An electronic map displayed on the screen of, for example, a navigation system or a computer may be a three-dimensional map that expresses features such as buildings three-dimensionally. The three-dimensional map is generally displayed by drawing three-dimensional models by, for example, perspective projection.
The three-dimensional map includes a large number of features, and the ground surfaces are also expressed by polygons. This results in a large number of three-dimensional models and may significantly increase the processing load for drawing a three-dimensional map. Especially in the case of drawing a birds eye view from the high viewpoint, the display range of the map covers a wide area, so that the processing load for the display may have a remarkable increase.
In order to reduce such processing load, a plurality of map data having different levels of details are used concurrently in the case of displaying a three-dimensional map and more specifically a birds eye view map. For example, Japanese Patent Nos. JP 4422125B and JP 3362533B disclose techniques both applied to display of a three-dimensional bird's eye view map, which vertically divide the map display range into two parts, use detailed map data to display a lower area close to the viewpoint and use wide-area map data having the lower level of details to display an upper area distant away from the viewpoint.